Luminosity masks: why raw HDR is the best HDR

In the latest post of our ongoing Raw Tuesday series on editing raw format images we show you a luminosity mask technique that enables you to create the perfect raw HDR image by blending two exposures according to lightness, not just area. This is a variation on the traditional HDR photography technique, but because we want to darken highlights and lighten shadows throughout the image rather than in selected areas, we’ll blend the images in a different way.

01 Create a well-exposed sky
To create a version of the image with a well-exposed sky, we’ve reduced Exposure to -0.40. Now we can open the edited image in Photoshop/Elements or save a copy before producing a second edit. By reopening the original file in Adobe Camera Raw if need be, and increasing Exposure to +2 and dropping Blacks to 2 or 3, we can produce the foreground exposure – you can go back later and try different Adobe Camera Raw settings at this stage if you like.

02 Rename the images
Now we can open this second edit in Photoshop/Elements (if we’d saved the edits out of Adobe Camera Raw, we’d open both from our desktop). We should also rename the images ‘sky1’ and ‘foreground1’ in case we want to produce more raw edits (bear in mind that if we tried this using a raw file in Elements, we wouldn’t be able to open the RAW file again unless we renamed the second version).

03 Combine the sky and foreground
Using the sky image, we Select All and Copy. Then on the shadows image, we Paste the sky image into the foreground document as a new layer. (In Elements, we’d see a bit-depth warning if the images were in 16-bit mode; you’d OK this to convert to 8-bit). The new layer is renamed ‘sky’ so we don’t get confused about which layer is which.

04 Make the selection
Now it’s time to create the luminosity selection that we’ll use to blend the two images. If we were using Photoshop Elements, we’d skip to steps 6 and 7 at this point. Using Adobe Photoshop though, we open the Channels palette and [Ctrl]/[Command]-click on the RGB channel. This action generates a selection of the sky layer’s highlights and light midtones.

05 Photoshop: Add the mask
With this selection active, we click the ‘Add layer mask’ button at the foot of the Layers palette. The layer mask will be based on the luminosity selection that we’ve just generated: the selected highlight areas of the upper layer will be revealed and its dark areas will be hidden, revealing the correctly-exposed shadow areas on the Background layer, which is the shadows image.

06 Elements: Create the mask
To create a luminosity mask in Elements, click the sky layer thumbnail and select Select All and Copy. Next, add a Levels adjustment layer, and OK the dialog without touching the sliders (from Elements 8, this will be the Adjustments panel rather than a dialog). To display the mask in the main image window, [Alt]/[Option]-click the mask thumbnail and paste the copied sky image.

07 Elements: Create a clipping mask
A grayscale version of the sky layer is now visible; the mask will be based on those grayscale values. A quick [Alt]/[Option]-click on the mask thumbnail enables us to view the image again. To apply the mask to the sky layer, we move the Levels layer beneath the sky layer in the stack, then [Alt]/[Option]-click the line between the two layers to create a clipping mask.